A plurality of different types of reel-ups exist for reeling a continuous paper web from a paper machine to a paper reel. These are usually designed with two separate systems in order to enable continuous production to be maintained, namely a primary system for receipt of an empty reeling drum from a pair of lowering arms upstream of the reel-up and, when the paper web has been wound a few turns, a secondary system which takes over the reeling drum with the beginnings of a paper reel for continued reeling to a finished reel of paper.
Examples of usual types of reel-ups are those in which the secondary system comprises either a pair of secondary arms or a pair of secondary carriages which are turned or displaced linearly depending on the increase in diameter of the paper reel. Reel-ups with secondary arms are described in the following patent specifications, for instance: U.S. Pat. Nos. 4,143,828, 4,283,023, 4,175,714, 3,614,011 and 5,520,354. Reel-ups with linearly movable secondary carriages are described in the following patent specifications, for instance: U.S. Pat. Nos. 4,934,619 and 5,370,327.
Another example is a slightly different and more modern type of reel-up which entirely lacks the primary system described above, but which is instead provided with double secondary units to replace said primary system. A reel-up of this type is described in U.S. Pat. No. 5,370,327.
In the present context we have chosen to use the prefix "secondary" in the terms "secondary system", "secondary unit", "secondary part", "secondary body", etc., even if the reel-up does not have a primary system.
In reel-ups of the first-mentioned type, i.e., with primary systems, reeling occurs briefly in the following way: An empty reeling drum is transferred from a stock of drums upstream of the reel-up to a pair of primary forks which bring it into contact with a driven surface winding drum over which the web runs, in order to initiate reeling of the web. Considerable friction thus occurs between the reeling drum and the surface winding drum, so that the reeling drum is generally first caused to rotate at the same speed as the surface winding drum before coming into contact with the drum.
The reeling drum is then moved along the periphery of the surface winding drum, down to horizontal stand members where secondary units in the form of secondary arms or secondary carriages take over control of the reeling drum. Continued reeling to a finished reel is achieved in that the secondary arms or secondary carriages, turning around a joint or being displaced linearly along the stand members, follow the horizontal movement of the reel caused by its increasing size. Press devices arranged on the secondary units, operate against bearing houses disposed on the end portions of the reeling drum so that a desired and adjustable linear pressure is maintained in the nip between the surface winding drum and the paper reel as it increases in size.
For certain grades of paper the linear pressure in the nip must be low in order to avoid negative properties in the paper reel. Too low a linear pressure will result in a risk that the individual layers in the reel will be wound too loosely. However, this problem can be solved by connecting the reeling drum to a central drive means with the aid of a coupling device disposed at one end of the reeling drum since the reeling drum no longer needs to be driven by the friction against the surface winding drum. Central driving also allows the linear pressure to be varied within a wider range so that the compression of the paper web in the nip between the paper reel and the surface winding drum can be reduced. Reel-ups with central driving are described in the following patent specifications, for instance: U.S. Pat. Nos. 4,934,619, 5,370,327, 5,520,354, 5,375,790 (SE-469 071) and 5,393,008 (SE-469 072).
When central driving is used for transferring the reeling drum from the primary system to the secondary system, a change of transmission must be effected between different drive devices, which affects the linear pressure due to a temporary pressure increase in the nip. To optimize reeling, the same driving may be connected throughout the reeling procedure from the start with an empty reeling drum, to finished reel. To achieve this it is previously known to use double sets of secondary carriages only, which alternate with each other and enable omission of the primary arms. In this way a single drive means connected to one of the carriage pairs can follow the reeling drum throughout the reeling process to a finished reel. A reel-up of this type is described in U.S. Pat. No. 5,370,327.
All these known reel-ups of various types, both with and without primary systems, suffer from another considerable common problem, namely that of undesired frictional forces. The reason these forces constitute such a great problem is that, as mentioned above, it is extremely important during the reeling procedure to be able to control the linear pressure in the nip between the surface winding drum and the growing paper reel as exactly as possible in order to avoid negative properties in the paper reel, particularly when reeling soft crepe paper such as "soft tissue" and similarly delicate paper used for sanitary purposes, which requires a low linear pressure. However, this control is made more difficult by said frictional forces. A reliable and correct control of the nip pressure thus requires a linear loading system with very little friction.
Undesired frictional forces arise, inter alia, due to friction in bearings and contact surfaces, friction in joints of the primary and secondary arms, press devices, etc. Friction may also arise in the hydraulic cylinders that move the secondary carriages. Every reel-up with secondary carriages also has one or more rails in its stand members, arranged to control the secondary carriage and to minimize the friction during the to and from movement of the secondary carriage. The latter is suitably effected through some form of bearings such as roller or slide bearings.
In a reel-up with a linear load system comprising horizontally movable secondary units for the reeling drum, it is the friction between the reeling drum and the stand rails, the stand-rail friction, which is responsible for the greatest limitation in accuracy and reliability in the control over the linear pressure in the reel nip. Even if the linear bearings of the secondary carriages are designed with very little friction, the stand-rail friction will be the same, regardless of any improvements in the bearings of the secondary carriage, i.e., unchanged high friction in this case, as long as the reel is supported by the stand rail during the production phase. Even in the case of very low frictional forces caused by the linear bearings, the stand-rail friction will still give relatively considerable negative effects on the properties of the paper reel, which may also affect the quality of the paper in other respects.
In the known reel-ups the reeling drum gives rise to at least three different cooperating frictional forces, namely a first friction in the bearing house caused by rotation of the reeling drum and by movement of the reeling drum along the stand rail as the reel increases in size, a second friction through abutment against the stand rail and finally a third friction in the linear bearings of the secondary carriage.
When the reeling drum runs along the stand rail during production of a new paper reel, there is a not negligible risk of obstacles in the form of foreign objects such as accumulated dust from the paper web, or deformities in the stand rail or the reeling drum, having a detrimental effect on the horizontal movement and causing temporary oscillations in the nip pressure due to the increased force that must be intermittently supplied to the actuators when the reeling drum encounters the obstacle, and this may have a negative effect on the paper reel. The uneven linear movement caused by said obstacles, including deformations in the form of surface damage to the stand rail, for instance, also gives rise to unfavorable vibrations, which affect the paper reel and in the long term may result in unnecessary wear on the bearing house of the reeling drum, for instance, and thus also on the coupling device for central driving of the reeling drum. When positioning the reeling drum along the stand as the paper reel increases in size, the stand friction constitutes an additional problem since it complicates the adjustments necessary for the actuators of the secondary unit.